Full-scale External Pressure Test of Used Nuclear Fuel Container for Deep Geological Disposal

Abstract

Many countries around the world are pursuing the implementation of a Deep Geological Repository (DGR) for the long-term storage of used nuclear fuel and high-level waste. For direct disposal of used fuel, the general concept consists of re-packing the fuel into long-lived Used Fuel Containers or Canisters (UFC). These containers are placed deep underground, typically over 400m in depth, and surrounded with clay sealing materials.Structurally, the container is designed to withstand the postulated loadings in the DGR including clay buffer swelling pressures, pore water pressures, and future glacial loading events. As a conservative worst case scenario, a maximum uniform external pressure of 45MPa is assumed from a combination of buffer swelling, fully saturated rock to DGR depths, and the hydrostatic head from a 3000m thick glacier directly over the repository.To ensure the container can withstand this extreme loading, a Finite Element Model (FEM) that can accurately predict the structural response of the container, including the non-linear buckling collapse load, was developed. An external pressure test of prototype container was performed at Penn State’s Advanced Research Laboratory High Pressure Test Facility to validate the model and container fabrication techniques. The container collapsed as predicted at approximately 57MPa. The validated model can now be used to predict the behaviour of the container in the DGR under normal evolution and beyond design basis loading scenarios. In addition, prototype fabrication including container machining and welding have been verified.